Add sparse_output option and control flags, and an output_not_seekable transfer flag, to structures for "sparse output" mode in future (#45).

src/include/options.h

@@ -88,6 +88,7 @@ struct opts_s {
 	bool no_splice;                /* flag set if never to use splice */
 	bool stop_at_size;             /* set if we stop at "size" bytes */
 	bool sync_after_write;         /* set if we sync after every write */
+	bool sparse_output;            /* set if we leave holes in the output */
 	bool direct_io;                /* set if O_DIRECT is to be used */
 	bool discard_input;            /* set to write nothing to output */
 	bool show_stats;	       /* set to write statistics at the end */

src/include/pv-internal.h

@@ -205,6 +205,7 @@ struct pvstate_s {
 		bool no_display;                 /* do nothing other than pipe data */
 		bool stop_at_size;               /* set if we stop at "size" bytes */
 		bool sync_after_write;           /* set if we sync after every write */
+		bool sparse_output;		 /* set if we leave holes in the output */
 		bool direct_io;                  /* set if O_DIRECT is to be used */
 		bool direct_io_changed;          /* set when direct_io is changed */
 		bool no_splice;                  /* never use splice() */
@@ -437,6 +438,7 @@ struct pvstate_s {
 		bool splice_used;
 #endif
 		bool read_error_warning_shown;
+		bool output_not_seekable;	/* set if lseek() fails on output */
 	} transfer;
 };